custom29scarab

Ferraristyle,
There is a 85 scarab 21 on e-bay right now that has the same motor guy has it listed as going 50mph so your speedo might be off a bit. I wouldn't expect much more with that set up.
Good luck and good boating.

tommymonza

I use to have an early 19 foot powerquest back in the early eighties with a stock 260 with thru-hull.Merury came down and propped it and it radared right at 59mph and when i raced all the 21 scarabs i had about a half a mph on them . I used to race a lot of them and they were all consistent in speed,so i think if your 260 is still healthy you should be right at 58.

Wobble

That whale tail is probably costing you some mph. Good for getting up on plane if thats a problem but it's a top end killer.

ferraristyle

I have some guys telling me 50MPH and others saying 57/58 MPH. That's a HUGE difference. What is the correct number? If the number is 50 then I'll probably be good on this run with the whale tail off and a lighter load (1 less adult; 2 less kids = 275lbs). I'm thinking that will get me close to the 50. But if 57/58 is correct then I have something wrong somewhere.

Is there any factory literature or numbers to verify what STOCK top speed was/is? Maybe some of the 21/22' Scarab guys could chime in and get a more accurate answer.

Anybody with the exact WOT top speed on this boat would be helpful.

tommymonza

Trust me on the 58 with two people and half a tank,but you should be turning 4600 not 5000 .Not enough prop?

ferraristyle

Which leads me into the question what size and pitch prop. I posted a link over at Prop Talk, but no one gets back with me. I don't know the gearing on the boat, but I have a Stern Drive "Chilton's" which I'm sure has it in it, just don't know what info I'm looking for.

Sent a PM to Julie over at Thottle Up but she hasn't gotten back with me either.

Any other prop vendors or prop people I can talk to or PM. Belive me, if the prop is what is holding me down; I'll be buying a new one tomorrow, just got to find out what size and pitch.

Help, direction, and comments appreciated.

bobonthis

One other thing to keep in mind also because I ran into this also is your tach might also be off. I had a 1990 23ft wellcraft nova that I could just never get dialed in right turns out just the tack was bad wouldn't ground right. just my .02 sometimes it is the little things.

tommymonza

I agree on the little things,could be you are running 55-58 and your speedo is lying which most likely it is .I have never had one half way accurate on a small v such as yours because most of the time your not in the water but on the drive at wide open.Do a gps reading first.

Your drive should be a 1.5 to 1 and i think the prop i ran was a 19x19 cleaver but not positive i'll check tomorrow.

also if the motor has some hours on it can run smooth but not have enough compression to produce the full 260hp.

ferraristyle

tommy

Thanks for the help so far. Just sort of disheartening that a relatively small boat with such a big engine only turns out in the 50's. Guess the hull and weight have a lot to do with it. Man, if this were a car I'd have no problem getting speed out of it, but I know cars, not boats which is an entirely different game.

Before last weekend I did a complete tuneup on the engine, everything except for timing and alignment which I'm getting done in two weeks. But I do have everything done including synthetic oil, new battery, plugs, distributor, wires, belts, fluids, etc.

I'm splashing the boat this weekend; trying to find someone with a portable GPS that will let me get a reading (anyone that lives near Annapolis, MD and wants to help me out with this PM me). Does anyone know of a place that rents one for a day?

I know for a fact that the large whale tail was holding me back some; but I didn't want to take it off before I knew what it did. (It's off now) Also know that I have to recheck my speedo tube, as last time I was out it kept folded up on me twice. Maybe this is the problem?? Man that would be an easy fix.

I also know that I was just about at 5K RPM wise at WOT; which is where my concerns for the prop come in. I should be 200-400 less. Bare in mind, since my boat was a movie/show/stunt boat, (I have the Miami Vice Action Spectacular Boat previously owned by George Barris of Batmobile fame) the boat has probably been set up for low speed not top end.

If worst comes to worst I'll have my friend run beside me on my 1100 Waveraider. On smooth water I easily hit 64 MPH with that so I could probably get a good estimate.

Finally, I'm bound and determined to change the prop. I know that this is part one of my issue. However before I go and spend $500 -$700 on an new prop I want to know what to get.

Sean H

pick up a cheap handheld gps, that will be your best tuning agent.... probably can find one for 100 bucks or so....

then test, test, test.... borrow some props if you can first before you buy anything... then change one thing and test some more....

nobody is gonna be able to tell you an exact speed because of water conditions, boat variance, driver inputs, weather conditions...

your next step is make sure you are making 260HP.... tune up, compression check...